Helmke Rebuttal
Bob Spector
Chairman, Working Group 3
Institute of Environmental Sciences
To the Editor:
As chairman of the Institute of Environmental Sciences Working Group 003, I feel the need to clarify several issues raised in the letter to the editor entitled, “Helmke Under Fire,” (Feedback, April 1996, p. 60). The referenced “Round Robin” tests that were performed by the committee were neither developed nor performed to produce a correlation between the Helmke Drum and the ASTM-F51-68 alternate method for accuracy or precision. The purpose of the test was to attempt to lower the limits previously established for the Helmke Drum Classification Chart, if possible.
Several omissions exist in the explanation of the ASTM Alternate Method. The procedure only allows testing a coverall. It is the only piece of apparel capable of being used because 1 ft2 of surface without seams is needed. The primary ASTM F51 procedure has five areas on the coverall, four in front, one in back, one area on the hood, and one to two on the boot, thus giving a thorough evaluation of the garment system. This is not possible using the alternate method. Be aware that alternate and/or modified versions of tests are typically to expedite testing not enhance the test.
The Helmke Drum is not necessarily the test of choice. Three test procedures for releasable or available particulate appear in the recommended practice. They are Particle Containment (Body Box), Helmke Drum and Primary Test Procedure (Modified from ASTM-F51 Alternate Method). Each of these tests will measure different aspects of the apparel. Particle Containment is used to determine relative differences between various sets of apparel when worn by an individual or individuals. Helmke Drum will count particles released at 0.5 microns or greater over a tumbling garment. The Primary Test Procedure is designed to measure particles 5.0 microns or larger, as well as fibers that are vacuumed off the surface of the fabrics. They each have their own role and function independently of each other.
If the customer is concerned about an accurate analysis of the contamination on his/her garments, then those customers should be sure the laundry that tests their garments uses a functional method of Statistical Process Control and/or Statistical Quality Control to monitor the trends associated with their garments.